Embodiments of the present invention are directed to apparatus and methods for reducing pressure and flow perturbations in fluid conduits. As used herein the term “pressure and flow perturbations” refer to rapid changes in the movement of fluid in a conduit or rapid changes in the pressure of fluid in a conduit. These flow and pressure perturbations may compromise “sample integrity”. As used herein, the term “sample integrity” refers to the desired composition of the sample. The boundaries of the sample become less sharp or distinct.
Aspects of the present invention are particularly useful in the field of chromatography. Chromatography is a chemical process in which compositions in solution (solutes) are separated from each other as the solution moves through a stationary material or phase. The compositions separate from each other based on the different affinity each composition has for the stationary phase. The solutions may comprise any fluid, such as, liquids, gases, supercritical fluids or mixtures thereof.
Chromatography is used to identify and quantify compositions held in a sample. The term “sample” is used herein to refer to any material that one desires to analyze.
High performance liquid chromatography, or HPLC, is a form of chromatography performed under pressure. The stationary phase is held in a column. A typical HPLC instrument may comprise a pump, conduits, sample injector, one or more columns and a detector. The solution is pumped through a conduit to a sample injector. At the sample injector, a sample is added to the solution in the conduit and conveyed to the column and through the stationary phase. Compositions in the solution separate as they traverse the stationary media in the column. The separated compositions are detected by a detector downstream of the column.
A typical HPLC instrument may operate at system pressures exceeding five thousand pounds per square inch (PSI). The term “system pressure” refers to the pressure in which the column operates. Recently, instruments have been introduced into the marketplace capable of operation at fifteen thousand PSI. Although the term HPLC refers to liquid, the principles of HPLC, for the purpose of this invention, apply equally to gases or supercritical fluids. Therefore, this document will use the term HPLC to refer to liquid, gas or supercritical fluid chromatography operating at pressures of up to five thousand PSI and up to and including extreme pressures of fifteen thousand PSI and above.
As used herein, the term “conduit” refers to pipes, tubes, capillaries, microfluidic channels, and the like.
The term “valve” refers to means to control, redirect, restrict or stop flow. The term “valve means” means one or more valves or moving a conduit to communicate with a different element of the instrument. For example, without limitation, sample injectors are often equipped with needles which are placed in fluid communication with vials containing sample and are able to move to different vials, solutions and other instrument stations. The term “sample injector” refers to a form of valve and conduits used to bring a section of conduit holding a sample into fluid communication with conduits upstream of a column. Sample injectors normally comprise multiport valves and a loop of conduit for holding a sample, needles and syringe pumps for withdrawing samples.
The term “column” refers to columns, cartridges, capillaries and the like for performing separations of a chromatographic nature. Columns are typically packed or loaded with a stationary phase. This stationary phase can be particulate or beadlike or a porous monolith or a substantially inert material. For the purpose of the present invention, the term “column” also refers to capillaries which are not packed or loaded with a stationary phase but rely on the surface area of the inner capillary wall to effect separations.
Solutions used in chromatography may take many forms and it is not unusual for the composition of the solution to change over the course of a separation. For example, it is often desirable to release components of a sample held on a stationary phase. By changing the composition of a solution flowing through the stationary phase, the components of the sample can be released. It is desirable to control the composition of the mixture such that the components of the sample are released in a reproducible manner.
It is difficult to maintain the integrity of a fluid sample in a conduit as flow is interrupted or the fluid experiences pressure disturbances.